It has been known for some time that drugs and medical instruments and implements have to be irradiated so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for irradiating drugs and medical instruments and implements. The drugs and the medical instruments and implements have then been stored in sterilized packages until they have been ready to be used.
In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor and foster the proliferation of such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as temperature. Some of the harmful bacteria can even be deadly.
For example, harmful bacteria have been discovered in recent years in hamburgers prepared by one of the large hamburger chains. Such harmful bacteria have caused a number of purchasers of hamburgers at stores in the chain to become sick. As a result of this incident and several other similar incidents, it is now recommended that hamburgers should be cooked to a well done, or at least a medium, state rather than a medium rare or rare state. Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. As a result of a number of incidents which have recently occurred, it is now recommended that all chickens should be cooked until no blood is visible in the cooked chickens.
To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to irradiate foods before the foods are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported into the United States from foreign countries.
In previous years, gamma rays have generally been the preferred medium for irradiating various articles. The gamma rays have been obtained from a suitable material such as cobalt and have been directed to the articles to be irradiated. The use of gamma rays has had certain disadvantages. One disadvantage is that irradiation by gamma rays is slow. Another disadvantage is that irradiation by gamma rays is not precise. This results in part from the fact that the strength of the source (e.g. cobalt) of the gamma rays decreases over a period of time and that the gamma rays cannot be directed in a sharp beam to the articles to be irradiated. This prevents all of the gamma rays from being useful in irradiating the articles.
In recent years, electron beams have been directed to articles to irradiate the articles. Electron beams have certain advantages over the use of gamma rays to irradiate articles. One advantage is that irradiation by electron beams is fast. For example, a hamburger patty having a square cross section can be instantaneously irradiated by a passage of an electron beam of a particular intensity through the hamburger patty. Another advantage is that irradiation by an electron beam is relatively precise because the strength of the electron beam remains substantially constant even when the electron beam continues to be generated over a long period of time. A further advantage is that the space occupied by the electrons and the direction of movement of the electrons can be precisely controlled since the electrons are in the form of a beam. A disadvantage is that the electrons can penetrate an article through only a limited distance. To increase the distance of penetration of the article, the electron beams can be directed to opposite sides of the article.
X-rays have also been used to irradiate articles. The x-rays may be formed from electron beams. An advantage in irradiating articles with x-rays is that the x-rays can irradiate articles which are thicker than the articles which are irradiated by electron beams. However, it would also be desirable to irradiate articles with x-rays from opposite sides of the articles to enhance the uniformity of the absorbed x-ray energy within the articles and to enhance the efficiency with which the x-ray energy is absorbed by the articles.
When an article is irradiated with radiant energy (e.g. electrons or x-rays) from opposite sides of an article, it would be desirable for the radiant energy to be obtained from a single accelerator. In this way, the radiant energy at the opposite sides of the article will be substantially identical so that each of the opposite sides of the article will receive substantially identical patterns of radiation. Furthermore, the costs will be minimized since accelerators are quite expensive.
The systems now in use for irradiating opposite sides of an article from a single accelerator have certain disadvantages. One disadvantage is that the systems require a large number of components each of which is quite expensive. Since there are a large number of components, there are a large number of controls for the components. Furthermore, these components and their controls occupy a large volume of space.